Usually, what happens:
- Your team is leading by a lot.
- Enemy team near-aces you, gains the advantage.
- Enemy team has lower respawn timers at this point.
- You'd need to form a coordinated attack and win a 4v4 to retake a point, or BD to peel the enemies off and go for one or the other then.
- Your team instead tries to finish it fast rushing to the points, getting picked off one by one maybe killing an opponent who's right back due to their reduced death timers.
- Your team is first relaxed, then in disbelief and finally demoralized, unable to play 100% for the entire duration of this chain of emotions.
- Enemy team rallies and pulls off the upset victory.
It's a fairly common occurrence. The map is designed to make those happen. It's specifically the reason the map stops losing points for anything but controlling majority at a point. It's designed to allow comebacks. You can bring opponent low with other stuff (note, killing creeps does NOT reduce enemy nexus points; it only gives you personal score) but finishing requires you to complete the map objective, that is to control the majority of the points.
This is why Dominion is never over until the last point is gone. I've seen over 400 point comebacks. Why? Because the winning team made mistakes, fell behind and played incoherently thinking their advantage allows them to play careless. Without systematic play, the low death timers are going to thwart your petty capture attempts.
If I lose like that, I look back at our team play, realize we had none and shrug. A team with high death timers can't afford to play carelessly. When you fall behind like that, you have to wait for all to respawn, group up and make a systematic push for a point. Your advantage gives you plenty of time, so don't rush things. Utilize your advantage to pad the attack and make the advantage count. You have enough gold advantage and probably half a level on your opponent at that point which should give you enough of an edge to win the fight.
If you were winning until then, you should be able to take one even fight when you're fully prepared for it (most teams will never understand to try this tho unless you spell it out the second they're down to under 10 and control 3). Unless your team is all early game while theirs is late and they just matured, in which case you're pretty ****ed and have to go for some serious map control shenanigans (lure 'em to traps in mid, backdoor with two, peel bot off, etc.) to have a chance.